Sound Attenuating Baffle Including a Non-Eroding Liner Sheet

ABSTRACT

A sound attenuating baffle device used in a duct receiving a gaseous flow in a flow direction therethrough, includes a baffle casing supported within the duct and a fibrous sound absorbing material occupying the hollow interior of the baffle casing. One or more perforated sheet members at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed. A liner sheet of a non-eroding, sound absorbing foam material is supported within the hollow interior of the baffle casing against an interior surface of the perforated sheet member(s) so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations to prevent erosion of the fibrous sound absorbing material into the gaseous flow through the duct.

This application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 62/312,661, filed Mar. 24, 2016.

FIELD OF THE INVENTION

The present invention relates to a sound attenuating baffle intended to be mounted within the duct of an air distribution HVAC system, a ventilation system, mounted directly to a fan or other air movement system for either air or gas streams in which the baffle is typically oriented in the flow direction through the duct. More particularly the present invention relates to a sound attenuating baffle the type including an outer baffle casing which is at least partially perforated and which contains fibrous sound absorbing material therein, and which is further provided with a liner sheet against an interior surface of the perforations in the outer baffle casing to prevent direct communication between the fibrous sound absorbing material and the perforations so as to prevent eroded fibrous sound absorbing material from being carried by airflow externally of the baffle casing through the perforations.

BACKGROUND

Silencers are used in air distribution HVAC systems, ventilation systems and other air movement systems for either air and gas streams. These products typically provide a duct section, for mounting in a duct system or directly to a fan, which support one or more baffle devices therein. Baffle devices are understood herein to comprise any rectangular, circular or other shaped object having a sound absorbing internal structure, typically using fibrous acoustic media fill, that may include, but not be limited to, fiberglass fiber, rock wool or natural cotton media. The media fill material provides a dissipation of the sound energy as it travels through the baffle device(s) of the silencer's duct section.

Rectangular cross-sectional silencers typically employ sound absorbing baffle devices in the form of rectangular sound absorbing elements such as baffles or splitters within a rectangular cross-sectional duct. Circular silencers may employ sound absorbing baffle devices either in the form of rectangular baffles or circular centerbody pods within circular cross-sectional duct. Rectangular silencers may include one baffle or several parallel baffles along the width of the duct or casing. The rectangular baffles or circular center body pods may be uniform along the casing length, or may be transitional where the inlet cross-section is not equal to the outlet cross-section. Silencer attenuation may be described as either a transmission loss (TL; dB) or an insertion loss (IL, dB). TL is a measure of the sound power upstream versus the sound power downstream from the silencer air opening(s). IL is a measure of the change in the sound level at a defined point of reception (e.g., outdoors, within a room, etc.) with and without the silencer installed.

Silencers with rectangular shaped baffle devices or circular centerbody baffle devices introduce aerodynamic losses due to the nature of the silencer orientation and installation conditions, resulting in blockage of the cross-sectional area, and aerodynamic friction and dump losses. The net aerodynamic losses are quantified as a total pressure drop or pressure resistance. Lower aerodynamic losses are desirable for most systems, as lower energy would be required to move a given volume or mass of air.

For systems that serve sensitive spaces (e.g., healthcare facilities, laboratories, etc.) and/or silencers with relatively high internal gap velocities (i.e., >4000 fpm), additional measures are required in order to avoid unwanted media erosion.

For the current state of art, thin films, typically Polyethylene or Polyvinyl materials at less than 0.08 inch thick, are used in silencers to protect the media fill. The film liner is positioned continuously between the media fill and the perforated metal liner. This type of media fill protection is considered advantageous towards human occupants, protection of the mechanical equipment, or both.

Thin film liners are not acoustically porous and generally do not provide any desirable absorptive properties. Thus, film liners significantly degrade the silencer attenuation, as it compares to a silencer internal geometry that applies media fill only. In order to achieve higher levels of sound attenuation, baffle device lengths and the quantity tend to increase significantly, due to this degradation in performance related to traditional film liners.

The present invention seeks to improve upon the construction design and installation of baffle type silencers in a unique fashion to improve the attenuation of the silencer in applications where a liner protection is required.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising:

a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing;

the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed;

a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and

a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations;

wherein the liner sheet is formed of a non-eroding, sound absorbing material.

Preferably, the liner sheet is formed of a sound absorbing foam material.

The foam material liner sheet provides a more stable, reliable and acoustically improved design for delivering protection against fibrous media erosion. Acoustic foam material is acoustically absorptive, with significantly higher noise reduction coefficients (NRC) as compared to film liners. The foam, either open cell or specially constructed closed cell material, has self-supporting properties allowing for improved installation quality and repeatability. When properly installed between the media fill and the perforated liner, a foam liner with a thickness greater than 0.125 inches offers improved acoustic performance with the desired media protection against erosion or breakdown of the silencer's absorptive media.

In preferred embodiments, a thickness of the foam material in a direction perpendicular to said at least one perforated sheet is between 0.125 and 2 inches so as to be less than 40% of a thickness of the fibrous sound absorbing layer in a direction perpendicular to said at least one perforated sheet.

The sound absorbing foam material may be either an open-cell or closed-cell foam and may comprise a melamine resin and/or a thermoset polymer, for example polyethylene.

Preferably the sound absorbing foam material continuously and fully spans said at least one perforated sheet member.

When the fibrous sound absorbing material is supported within the hollow interior of the baffle casing under resilient compression, preferably the liner sheet is supported against the interior surface of said at least one perforated sheet member by the resilient compression of the fibrous sound absorbing material.

The baffle casing may further include at least one support flange overlapping at least a portion of a perimeter edge of the liner sheet so as to retain the liner against the interior surface of said at least one perforated sheet member.

When the baffle is suspended at an intermediate location with the duct, in the instance of a full baffle, the baffle casing comprises two opposed faces having i) a length spanning in a longitudinal direction between a leading end and a trailing end of the baffle casing, ii) a width spanning in a lateral direction between opposing sides of the baffle casing, and iii) a thickness between the two opposed faces which is reduced in dimension relative to the length and the width, the baffle casing being adapted to be supported within the duct such that the longitudinal direction is aligned with the flow direction. In this instance said at least one perforated sheet member consists of two perforated sheet members defining the two opposed faces of the baffle casing respectively such that the liner sheet spans the interior surface of each of the two opposed faces of the baffle casing.

Alternatively, when the baffle device is a half-baffle supported against a solid boundary wall of the duct, the baffle casing may only comprise a single perforated sheet member across which the gaseous flow is directed so that only a single liner sheet fully spanning the single perforated sheet member is required in this instance.

According to another aspect of the present invention there is provided a sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising:

a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing;

the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed;

a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and

a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations;

wherein the liner sheet is a membrane of sound absorbing material.

According to a further aspect of the present invention there is provided a sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising:

a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing;

the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed;

a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and

a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations;

wherein the liner sheet is formed of a sound absorbing foam material.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an exemplary duct locating a silencer comprising sound attenuating baffles according to the present invention therein;

FIG. 2 is a schematic sectional view along the line 2-2 of FIG. 1;

FIG. 3 is a schematic sectional view along the line 3-3 of FIG. 2 of a plurality of baffles; and

FIG. 4 is a detailed sectional view along the line 3-3 of FIG. 2 of a single intermediate baffle.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures there is illustrated a sound attenuating baffle device generally indicated by reference numeral 10. The device 10 is particularly suited for use in a silencer apparatus for attenuating sound in a ducted flow. The duct may be any suitable size or shape for receiving a flow of air or gas therethrough in a flow direction of the duct in air distribution HVAC systems, ventilation systems and other air movement systems for either air and gas streams.

In the illustrated embodiment, the duct is a transitional duct section 12 having a rectangular cross-section which tapers to be reduced in cross-sectional area from an inlet end 14 to an outlet end 16. In further embodiments however, the sound attenuating baffle device 10 can be readily applied to any other type of duct including duct sections with circular cross-sections, a straight duct section, or an elbow duct section while still achieving the benefits described herein. The flow direction through the duct is understood herein to correspond to the direction that air moves through the duct. In a straight or transitional duct, the flow direction is typically linear from the inlet to the outlet end of the duct; however, in an elbow duct, the flow direction is understood to follow a generally curved path from the inlet to the outlet of the duct.

The duct section 12 of the silencer apparatus is mounted within a duct system or directly to a fan, and is comprised of one or more baffle devices 10. In the illustrated embodiment, the silencer apparatus mounted within the duct 12 comprises one half-baffle device 10A mounted against one boundary wall of the duct section 12 and two intermediate baffle devices 10B which are mounted at respective intermediate locations within the duct section. The baffle devices 10A and 10B are all generally parallel and spaced apart from one another within the perimeter boundary of the duct.

Each baffle device 10 extends in a lateral direction across a full width of the duct between two opposing sides 18 of the baffle. Each baffle also extends in a longitudinal direction generally parallel to the flow through the duct from a leading end 20 of the baffle device to a trailing end 22. The baffle device is generally uniform in shape in the lateral direction across the full width. A thickness of the baffle device, measured perpendicularly to both the lateral and longitudinal directions, tapers in the flow direction so as to be reduced in overall thickness from the leading end 20 to the trailing end 22.

Each baffle device includes an outer baffle casing 24 in the form of a shell which defines the outer boundary of the baffle device. The outer baffle casing 24 of the half baffle 10A is approximately one half of the overall shape and size of each intermediate baffle device 10B according to the illustrated embodiment.

With regard to each intermediate baffle device 10B, the outer baffle casing 24 includes a first cap 26 spanning laterally across the full width of the baffle device at the leading end. The first cap 26 is formed of sheet metal and is generally concave at the outer side in the direction of the thickness of the baffle, while extending generally linearly across the full width of the baffle in the lateral direction with a uniform profile. The first cap 26 is typically formed to be devoid of perforations so as to be generally domed and aerodynamic in shape. In the illustrated embodiment mounting flanges 28 are formed at opposing ends of the first cap 26 for mounting two opposing side walls of the surrounding duct, however in further embodiments various other means may be used to support the baffle device relative to the duct.

The outer baffle casing 24 further comprises two opposed faces comprising perforated metal sheet members 30 which are generally planar in shape for spanning the full width and substantially the full length of the outer baffle casing. The overall thickness of the baffle is defined by the distance between the two opposed faces.

A second cap 32 is mounted between the perforated sheet members 30 at the trailing end of the baffle device to span the full width between opposing sides of the duct and to span the full thickness between the opposing faces. The second cap 32 may be planar in shape, oriented perpendicularly to the flow direction through the duct. Mounting flanges 34 are also provided at opposing ends of the second cap 32 for mounting to opposing side walls of the duct according to the illustrated embodiment, however in further embodiments various other means may be used to support the baffle as noted above. The second cap 32 in the illustrated embodiment is a solid panel.

The perforated sheet members 30 defining the two opposed faces of each baffle device 10B are oriented generally in the flow direction, however, the faces are sloped by a few degrees relative to the flow direction such that the two opposed faces taper towards one another to reduce the overall thickness therebetween in the flow direction from the first cap 26 at the leading end to the second cap 34 at the trailing end.

A hollow interior of the resulting outer baffle casing 24 is filled with a sound absorbing material 36 which defines a sound absorbing layer occupying most of the thickness of the outer baffle casing. Sound absorbing materials suitable for use with the present invention include lightweight, porous or loose fill materials such as fibrous material including fiberglass, mineral wool, or natural cotton media for example, which have the ability to dissipate sound energy travelling therethrough.

The half baffle device 10A is similar to the intermediate baffle devices 10B in that there is provided an outer baffle casing 124 which also forms the shell which defines the outer boundary of the baffle device. The outer baffle casing 124 again includes a first cap 126 spanning across the full width of the baffle device at the leading end so as to spend the full thickness of the baffle device. The first cap 126 is formed of sheet metal and is concave at the outer side, but corresponds approximately to only half of the profile of the first cap of the intermediate baffle devices. Mounting flanges 128 are formed at opposing ends of the first cap 126 for mounting two opposing side walls of the surrounding duct section.

The half baffle device 10A also includes a second cap 132 mounted at the trailing end of the baffle device to span the full width between opposing sides of the duct and to extend the full thickness of the baffle device the second cap 132 is oriented generally perpendicularly to the flow direction through the duct section.

The half baffle device 10A also includes a perforated metal sheet member 130 which spans the full width of the duct section and which extends substantially the full length of the outer baffle casing 124 between the first cap 126 at the leading end and the second cap 132 at the trailing end of the baffle device. The overall thickness of the baffle is defined by the distance between the perforated sheet member 130 and the adjacent boundary wall of the duct section in the instance of the half baffle device.

The hollow interior of the resulting outer baffle casing 124 of the half baffle device 10A is also filled with a sound absorbing material 136 which defines a sound absorbing layer occupying most of the thickness of the outer baffle casing. As noted above, sound absorbing materials suitable for use with the present invention include lightweight, porous or loose fill materials such as fibrous material including fiberglass, mineral wool, or natural cotton media for example, which have the ability to dissipate sound energy travelling therethrough.

In the instance of either a full baffle device 10B or a half baffle device 10A the perforated metal sheet member 30 or 130 defines a substantial portion of the exterior of the baffle casing which is oriented generally in the flow direction of the duct section and across which the gaseous flow through the duct section is directed in use. Each of the perforated sheet members includes a plurality of perforations formed therein. The perforations in the sheet members typically comprise the only openings in the overall shell formed by the baffle casing. To prevent communication of the fibrous sound absorbing material occupying the hollow interior of each outer casing, a sound absorbing foam material liner sheet 150 is supported on the interior surface of each perforated sheet member 30 and 130. The liner sheet 150 spans across each of the perforations to prevent direct communication of the fibrous sound absorbing material with the perforations.

In the illustrated embodiment each perforated sheet member 30 and 130 is provided with a single continuous liner sheet 150 which spans the full length and the full width of the sheet member directly against the interior surface thereof. In further embodiments the liner sheet 150 may be formed in sections which are abutted with one another or joined at respective scenes by various means, however careful attention is required to prevent any gaps at the seams between adjacent sections of liner material which might communicate with any perforation in the sheet member in this instance.

The liner sheet 150 is formed of a foam material, either open-cell or closed-cell. In the illustrated embodiment the foam material is a melamine resin, thermoset polymer, for example polyethylene. The liner sheet can be any membrane or sheet-like material capable of forming a layer, devoid of any openings, and which is non-eroding, and preferably non-fibrous, while remaining sufficiently resilient to be more sound absorptive than reflective.

Thickness of the foam material sheet in a direction which is perpendicular to the perforated sheet member against which the foam liner sheet is supported is in the range of 0.125 to 2 inches. The thickness of the foam material is thus generally less than 40% of an overall thickness of the fibrous material forming the sound absorbing layer, and is preferably in the range of 5 to 10% of the overall thickness of the fibrous material forming the sound absorbing layer.

The fibrous sound absorbing material typically occupies the remainder of the hollow interior of the outer baffle casing not occupied by the foam liner sheet(s) 150 and is supported within the hollow interior under resilient compression. The compression of the fibrous sound absorbing material applies outward pressure to the liner sheet 150 to support the sheet pressed against the interior surface of the corresponding perforated sheet member 30 or 130 across substantially the full width and full length of the sheet member.

To provide additional support at the perimeter edges of the liner sheet 150, support flanges 152 may be mounted within the interior of the baffle casing which overlap a portion of the liner sheet adjacent to the perimeter edge such that the edge portion of the liner sheet is retained between the support flange and the perforated sheet member. The support flanges 152 may be part of respective L-shaped or Z-shaped structural pieces mounted against the interior surface of the perforated sheet members to extend along respective ones of the perimeter edges of the liner sheets.

Since various modifications can be made in my invention as herein above described, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising: a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing; the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed; a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations; wherein the liner sheet is formed of a non-eroding, sound absorbing material.
 2. The baffle device according to claim 1 wherein the liner sheet is formed of a sound absorbing foam material.
 3. The baffle device according to claim 2 wherein a thickness of the foam material in a direction perpendicular to said at least one perforated sheet is between 0.125 and 2 inches.
 4. The baffle device according to claim 2 wherein a thickness of the foam material in a direction perpendicular to said at least one perforated sheet which is less than 40% of a thickness of the sound absorbing layer in a direction perpendicular to said at least one perforated sheet.
 5. The baffle device according to claim 2 wherein the sound absorbing foam material comprises an open-cell foam.
 6. The baffle device according to claim 2 wherein the sound absorbing foam material comprises a closed-cell foam.
 7. The baffle device according to claim 2 wherein the sound absorbing foam material comprises a melamine resin.
 8. The baffle device according to claim 2 wherein the sound absorbing foam material comprises a thermoset polymer.
 9. The baffle device according to claim 2 wherein the sound absorbing foam material comprises polyethylene.
 10. The baffle device according to claim 1 wherein the liner sheet fully spans said at least one perforated sheet member.
 11. The baffle device according to claim 1 wherein the fibrous sound absorbing material is supported within the hollow interior of the baffle casing under resilient compression and wherein the liner sheet is supported against the interior surface of said at least one perforated sheet member by the resilient compression of the fibrous sound absorbing material.
 12. The baffle device according to claim 1 wherein the baffle casing includes at least one support flange overlapping at least a portion of a perimeter edge of the liner sheet so as to retain the liner against the interior surface of said at least one perforated sheet member.
 13. The baffle device according to claim 1 wherein the baffle casing comprises two opposed faces having i) a length spanning in a longitudinal direction between a leading end and a trailing end of the baffle casing, ii) a width spanning in a lateral direction between opposing sides of the baffle casing, and iii) a thickness between the two opposed faces which is reduced in dimension relative to the length and the width, the baffle casing being adapted to be supported within the duct such that the longitudinal direction is aligned with the flow direction; and wherein said at least one perforated sheet member comprises two perforated sheet members defining the two opposed faces of the baffle casing respectively such that the liner sheet spans the interior surface of each of the two opposed faces of the baffle casing.
 14. A sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising: a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing; the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed; a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations; wherein the liner sheet is a membrane of sound absorbing material.
 15. A sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising: a baffle casing having a hollow interior and being adapted to be supported within the duct such that the gaseous flow is directed across an exterior of the baffle casing; the baffle casing including at least one perforated sheet member having a plurality of perforations therein which at least partially defines the exterior of the baffle casing across which the gaseous flow of the duct is arranged to be directed; a sound absorbing layer formed of fibrous sound absorbing material occupying the hollow interior of the baffle casing; and a liner sheet supported within the hollow interior of the baffle casing against an interior surface of said at least one perforated sheet member so as to span across each of the perforations and prevent direct communication of the fibrous sound absorbing material with the perforations; wherein the liner sheet is formed of a sound absorbing foam material. 